a) Field of the Invention
The present invention relates to a seal-less canned motor pump, and more particular to structural improvement of a canned motor pump which is used especially in a plastic pump or a pump with plastic lining to transfer, pressurize and circulate high corrosive chemical liquids. Process chemical liquids are very corrosive, in addition that some of the liquids temperature could reach 85° C. in manufacturing processes at atmosphere pressure, the stiffness of plastic parts will be decreased significantly and deformation will be formed. For the conventional plastic or plastic lining seal-less canned motor pump with stationary shaft, which could be both-end supported or cantilever, the both-end supported shaft has a front shaft holder and a containment shell holder, and the cantilever one has a strengthened containment shell holder only. Owing to all the above structures are with lower stiffness, therefore reliability and performance will be reduced in a great deal. The structural improvement disclosed by the present invention is able to improve the reliability and lifetime of operation.
b) Description of the Prior Art
A metallic seal-less canned motor pump is applied in many industries today, the motor is induction motor or permanent magnet motor, this kind of pump is especially designed for corrosion-resistance and leak-proof applications, most of their structure of motor are with rotational shaft and supported by bearings at both ends of motor flanges. But some of the seal-less canned motor pump are made of plastic or with plastic, lining, hereafter call it plastic seal-less canned motor pump for highly corrosion-resistance and leak-proof applications, for example, precise etching process in PCB manufacturing a metallic seal-less canned motor pump cannot serve for the application, and some features of the plastic seal-less canned motor pump inherit from plastic seal-less magnetic coupling pump, some of them are stationary shaft design and containment shell structure, and the plastic seal-less canned motor pump is integrated with permanent magnet motor to replace the conventional induction motor and the magnetic coupling. The objects of the plastic seal-less canned motor pump are to have smaller size to save installation space, higher performance motor to improve application range of the pump and less parts to increase reliability; moreover, as it is easier to adjust discharge flow rate and head by adjusting rotation speed, and, thereby better satisfying a wider requirement in the manufacturing process.
Referring to FIG. 1, a conventional permanent magnet canned motor pump includes a stationary shaft supported at both shaft ends. The pump comprises a pump casing 4, an impeller 5, a containment shell 41, a stationary shaft 3, a front shaft holder 31 and a canned motor 8; wherein, the pump casing 4 is provided with an inlet 44, an outlet 45 and a flow channel 47, which is used to install the impeller 5. An inlet thrust ring 46 is provided in an interior side of the pump casing 4 at the inlet 44, to couple with an impeller wear ring 53 at the inlet side of the impeller 5, constituted as an axial thrust bearing.
The front shaft holder 31 is fixed at entrance of the pump casing 4 and axially penetrated through hole 54 on the impeller hub 52 to support front end of the stationary shaft 3.
The impeller 5 is installed inside the pump casing 4, impeller huh 52 is a collar structure which is axially extended backward and is used to conjunct with an axially extended part 76 of a motor rotor 7, thereby constituting the impeller 5 and the motor rotor 7 as one integral rotational unit; in many conditions, the motor rotor 7 and the impeller hub 52 are made as one unit by plastic injection directly.
The containment shell 41 of the canned motor 8 is a cup-shape structure, and the front-end flange 411 is combined with the pump casing 4 and the flange 811 of the motor 8 to prevent corrosive liquid from leakage and to enhance a sealing ability. A column part 412 of the containment shell 41 is sheathed into an inner circumference of the motor stator 83 to isolate corrosive liquid, thereby preventing the motor winding 831 from being corroded. The central part of bottom of the containment shell 41 provides with a containment shell holder 413, a recessed blind-hole structure, to support the other end of the stationary shaft 3 and to fix a thrust bearing 414 at the containment shell 41; An inner space 415 of the containment shell 41 is used to install the stationary shaft 3 and the motor rotor 7.
The stationary shaft 3 is supported at both ends and is made of ceramic material which is corrosion resistant and abrasion resistant, both ends of which are supported and fixed respectively by the front shaft holder 31 and the containment shell holder 413, and a central part of which is coupled with bearings 77, 78 to support rotation of the motor rotor 7.
The canned motor 8 comprises a motor stator 83, a motor casing 81, a motor rear casing 82, a containment shell 41, a motor rotor 7 and a stationary shaft 3, wherein the motor stator 83 is installed in the motor casing 81, the motor rear casing 82 is fixed on the motor casing 81. A central part of the motor rear casing 82 is provided with a recessed shaft support seat 821, to fix the containment shell holder 413 on the containment shell 41, to enhance supporting intensity of the stationary shaft; and a flange 811 at the pump side of the motor casing 81 is used to tightly lock the flange 411 and the pump casing 4 together, so as to prevent corrosive liquid from leakage. The motor stator 83 and stator winding 831 are completely sealed by the containment shell 41 to prevent from leakage and contacting with corrosive liquid. The lower side of the motor rear casing 82 is provided with an exit port 822 of electric power cable, such electric power cable of a motor driver can be connected with the stator winding 831 to drive the motor 8.
The motor rotor 7 is made of a set of permanent magnets 71 and a yoke of rotor 72 made of silicon steel sheet metal, after being assembled, it is enclosed by a plastic material with corrosion-resistant properties to form a seam-less collar-shape encapsulated rotor 74. A hollow part of the rotor 7 is provided with two bearings 77 and 78 to couple with the stationary shaft 3, forming a hydraulic bearing system to support rotation and power transmission of the rotor 7. The axially extended part 76 is a part of the rotor 7 with rigidity and intensity properties in cylindrical structure, conjunct with the impeller hub 52 to effectively transfer power from the rotor 7, in many conditions a motor rotor 7 and the impeller huh 52 are made as one integral unit by plastic injection directly.
Referring to FIG. 2, another embodiment of a conventional permanent magnet canned motor pump with a cantilever shaft; the pump comprises a pump casing 4, an impeller 5, a containment shell 41, a stationary shaft 3 and a canned motor 8, wherein the pump casing 4 has an inlet 44, an outlet 45 and a flow channel 47, which is for the installation of impeller 5. An inlet thrust ring 46 is provided in an interior side of the pump casing 4 at the inlet 44, to couple with an impeller wear ring 53 at an inlet side of the impeller 5, constituting an axial thrust hearing.
The impeller 5 is installed inside the pump casing 4, and an impeller hub plate 55 is provided with plural holes 54 to serve as circumfluence holes for internal lubricant circulation and to serve as balance holes for removing axial thrust force, as well. An impeller hub 52 is a collar structure which is extended axially backward and is conjunct with an axially extended part 76 of a motor rotor 7, thereby constitutes the impeller 5 and the motor rotor 7 as one integral unit; in many conditions, the motor rotor 7 and the impeller hub 52 are injected integrally as one integral unit.
The containment shell 41 of the canned motor 8 is a cup-shape structure; the front-end flange 411 is combined with the pump casing 4 and the flange 811 of the motor 8 to prevent corrosive liquid from leakage and to enhance a sealing ability. A column part 412 of the containment shell 41 is sheathed into an inner circumference of the motor stator 83 to isolate corrosive liquid, thereby preventing the motor winding 831 from being corroded; at the bottom of the containment shell 41 is reinforced by a completely enclosed rigid structure member 416, wherein a central hole of the rigid structure member 416 is used to hold and to support one end of the stationary shaft 3; an inner space 415 of the containment shell 41 is used to install the stationary shaft 3 and the motor rotor 7.
The stationary shaft 3 is a cantilever shaft supported at one end by a shaft holder 416 in containment shell 41, made of a ceramic material which is corrosion resistant and abrasion resistant, and the shaft holder 416 is a rigid structure member enclosed at the bottom of the containment shell 41; and the central part of the stationary shaft 3 is coupled with the bearings 77, 78 to support the rotation of the motor rotor 7.
The canned motor 8 comprises a motor stator 83, a motor casing 81, a motor rear casing 82, a containment shell 41, a motor rotor 7 and a stationary shaft 3. The motor stator 83 is installed in the motor casing 81, the motor rear casing 82 is fixed on the motor casing 81. The flange 411 of the containment shell 41 is pressed by the pump casing 4 and a flange 811, at pump side of the motor casing 81, to tightly lock the flange 411 and the pump casing 4 together, so as to prevent corrosive liquid from leakage. The stationary shaft 3 is a cantilever shaft that supported at one end by a shaft holder 41 in containment shell 41, and the shaft holder 416 is a rigid structure member that enclosed at the bottom of the containment shell 41. The motor stator 83 and a stator winding 831 are completely sealed by the containment shell 41 to prevent from leakage of and contact with corrosive liquid. An underside of the motor rear casing 82 is provided with an exit port 822 of electric power cable; such electric power cable of a motor driver can be connected with the stator winding 831 to drive the motor 8.
The motor rotor 7 is made of a set of permanent magnets 71 and a yoke of rotor 72 made of silicon steel sheet metal, after assembled it is enclosed by a plastic material with corrosion-resistant properties to form a seam-less collar-shape encapsulated rotor 74. A hollow part of the rotor 7 is provided with two bearings 77 and 78 to couple with the stationary shaft 3, forming a hydraulic bearing system to support rotation and power transmission of the rotor 7. The axially extended part 76 is a part of the rotor 7 with rigidity and intensity properties in cylindrical structure, conjunct with the impeller hub 52 to effectively transfer power from the rotor 7, in many conditions the motor rotor 7 and the impeller hub 52 are injected integrally as one integral unit.
Referring to FIGS. 1 and 2, when the canned motor 8 is operating, fluid flows along a flowing direction 6 through a flow channel of the impeller 5 to become pressurized fluid, and along a flowing direction 61 and then exits from the outlet 45. In the meantime, part of fluid flows along a flowing direction 62 to enter into the inner space 415 of the containment shell 41, through the back side of the impeller 5, and flows toward the end plate of the containment shell 41 through a gap between the exterior side of the rotor 7 and the inner diameter of the containment shell 41, along a flowing direction 63 then turn around at the bottom of containment shell 41. Next, fluid flows through a gap between the stationary shaft 3 and the bearings 77 and 78 along a flowing direction 64, and finally flows through the holes 54 on the impeller hub 52 to return to the impeller inlet, along a flowing direction 65. This circulation of fluid is used to provide lubrication for the ceramic hearing and remove heat released by the rotor 7 and bearings 77 and 78.
The permanent magnet canned motor pump uses the winding 831 of the motor stator 83 to provide a rotational magnetic field and to interact with a permanent magnetic field of the motor rotor 7 to produce a torque and rotation by a driving method, which is different from the seal-less magnetic drive pump directly coupling an internal rotor with an external rotor of permanent magnet to drive. As the magnetic intensity generated by the winding 831 is dependent on electric current and coils number of the induction winding, which needs a larger size than the permanent magnet to produce a sufficient magnetic flux from stator, and costs money to increase the size of the permanent magnet of the motor rotor 7 also, owing to the structure of the motor rotor 7 should fit with the winding 831 of the motor stator 83 to get a better effect, the size of motor rotor will become larger and more weight also. Nevertheless, it also means that the stationary shaft 3 of the motor 8 will need to carry more loadings of centrifugal force resulted from the more weight of the motor rotor 7. These loadings of centrifugal force come from both residual unbalance of the motor rotor 7 it-self and an eccentric value produced by a gap of bearing 77 and 78 when pump is operating.
From the prior art as the stationary shaft 3 is supported by the plastic parts with lower structural stiffness, an issue of insufficient structural stiffness will be confronted with frequently, especially that if the temperature of transferred liquid goes up to 85° C. Furthermore, due to the differentials in thermal deformation between the plastic member and the ceramic member, and that will reduce the supporting force on the stationary shaft 3 a lot or increase deflection from fixed position of the stationary shaft 3. For instance, the front shaft holder 31 for both end support of the stationary shaft 3 is an obvious example, the structure stiffness of the front shaft holder 31 will be decreased at high temperature, resulting in an increasing eccentric value, and the containment shell holder 413 on containment shell 41 has the same conditions also. Regardless of supporting the stationary shaft 3 at both sides or using the cantilever to support the stationary shaft 3, as the containment shell 41 is thinner at the column part 412, the deformation will be produced easily by fluid temperature or pressure. Although the column part 412 is supported by an inner circumference of the motor stator 83, the fixed position at the bottom of the containment shell 41 of the stationary shaft 3 will still easily be affected resulting in an off-position. When temperature or pressure increases up to that the containment shell 41 can be deformed, the stationary shaft 3 will not be tightly combined with both the front shaft holder 31 and the containment shell holder 413 and get loosened. The other reason of the shaft loosening caused is from the differentials in thermal property between the plastic material and the ceramic material, which results in the stationary shaft 3 loosened.
The permanent magnet canned motor pump is driven by a controller, which could keep motor running in synchronization. The pump rotational speed could be or less than the rated speed in most conditions, but in lower discharge capacity conditions the rated rotation speed could be properly exceeding, those conditions are the output power or the output torque of the permanent canned motor 8 is within a reasonable range and not over limitations. When pump is operated at low rotational speed, it is not necessary to pay attention on the deformation and the centrifugal force issues, but it needs to be concerned if the speed is over the rated rotational speed. However, the centrifugal force applying on the stationary shaft 3 will be increased in squares of the rotation speed, more centrifugal force will get more deformation.
Concluding from the operating requirements of the pump described above, the core issues that need to face with for the application of a high corrosive manufacturing process are:                (1) The issue is the insufficient combining stiffness due to the differentials in thermal properties between the plastic material and the ceramic material;        (2) The issue of decreased intensity of the plastic material under high temperature; and        (3) The issue of increased centrifugal force when the operating speed exceeds the rated speed.        
To solve the aforementioned issues, the detailed causes of each issue should be analyzed so that the issue can be solved completely. The analyses of the issues are provided as follows:
(1) For the insufficient combining stiffness between plastic and ceramic issue: many corrosion-resistance plastic materials do not have a good physical property to resist thermal deformation and therefore, cannot maintain a tight combination with the ceramic material. However, an additional reinforce structure will be needed.                (2) For the structure stiffness of the plastic material issue: some plastic will be still provided with strong intensity when temperature increases, but their corrosion-resistance is insufficient. The intensity of many corrosion-resistance materials cannot compare with that of the ceramic material, especially that the intensity of material will be decreased significantly when temperature increases. Therefore, a brand new concept about the structure of shaft will be needed.)        (3) For the centrifugal force of motor rotor at high speed issue: as the motor rotor is heavy in mass with a residual unbalance or an eccentric in radius, and the necessary gap in radius for lubrication between the hydraulic bearings and the stationary shaft will increase the centrifugal load of stationary shaft that is the load of centrifugal force on the stationary shaft could be calculated as the mass of motor rotor times the centrifugal acceleration of the rotation, and the centrifugal acceleration of rotation is calculated as the total eccentric radius of rotor times the angular velocity in square, the total eccentric radius is the eccentric radius of unbalance of rotor plus the eccentric radius of the hydraulic bearings. However, a higher stiffness of the stationary shaft and a lower mass of motor rotor will be needed.        
There already have related solutions disclosed to solve the aforementioned issues.
The British patent GB2417981 discloses a stationary shaft structure which is a cantilever shaft structure, that at the bottom of the containment shell, a high-rigidity structure member is injected with the stationary shaft to tightly combine the plastic material with the stationary shaft and to improve the supporting strength of the shaft. Some of the wetting parts, like the flange of the containment shell, made of metal material is injected with plastic material; the plastic material used by the referred patent is engineering-grade plastic which is high temperature-resistant and is with high stiffness, but this material cannot withstand high corrosive fluid such as hydrofluoric acid. Because the application of the referred patent is used in cooling water for an engine cooling, there is no corrosion-resistance issue. Secondly, as the thickness of the column part of the containment shell is thin, the stiffness is insufficient to support the load of stationary shaft, which will easily cause the stationary shaft to be displaced or off-positioned.
However, the structure has good solution by using combining materials at the bottom of the containment shell and high temperature applications, but unable to solve structure stiffness issue at the column part of the containment shell and do not meet the requirement of high corrosion application also.
Another solution, the Japanese patent JP2005299559 discloses a stationary shaft structure which is supported at both shaft ends, that uses a front shaft holder at the inlet of the pump casing and a rear shaft holder at the bottom of the containment shell with an additional rigid structure member to intensify. This referred patent focuses on the design to reduce the weight of the rotor and this feature can effectively solve the centrifugal force problem of the rotor, because lower centrifugal force means lower stiffness demand of the stationary shaft. However, the structure is still unable to solve the combining stiffness issue and structure stiffness issue in high corrosion and high temperature applications. The referred patent is only used in the circulation of cooling water in an engine, while not with the corrosive liquid.
As the solutions described above are unable to provide a complete solution to the manufacturing process of high corrosive liquid, a better solution is provided by the present invention to satisfy requirements of the aforementioned issues.